How does uniapp determine whether there is a cache?

In the process of mobile application development, performance issues have always been one of the focuses of developers. Considering user experience, we usually use caching to optimize mobile applications. For applications developed using the uniapp framework, how do we determine whether the cache exists?

First, let us understand the caching mechanism of uniapp. uniapp uses the native caching mechanism of WeChat applet, namely WeChat applet Storage API. We can use the API encapsulated by uniapp to operate on Storage, as shown below:

// 保存数据到Storage中
uni.setStorageSync('key', 'value')

// 从Storage中读取数据
let data = uni.getStorageSync('key')

// 清空Storage
uni.clearStorageSync()

// 删除Storage中指定key的数据
uni.removeStorageSync('key')

Here, we use setStorageSync to store data into Storage; use getStorageSync to read data from Storage; use clearStorageSync to clear Storage; Use removeStorageSync to delete the specified key data in Storage.

Next, let's take a look at how to determine whether the cache exists. We can use the getStorageSync method. If the method returns undefined, it means that the cache item does not exist. For example:

let data = uni.getStorageSync('key')
if(data === undefined) {
  // 缓存项不存在
} else {
  // 缓存项存在
}

When using getStorageSync to read a key that does not exist, the returned value is undefined, so we can use it as a basis to determine whether the cache exists.

In addition, we can also use another method getStorageInfoSync provided by the Storage API to obtain all keys in the current Storage, and then traverse the key array to find whether the required cache item is in it. For example:

let info = uni.getStorageInfoSync()
let keys = info.keys
if(keys.indexOf('key') === -1) {
  // 缓存项不存在
} else {
  // 缓存项存在
}

Here, we use getStorageInfoSync to obtain Storage information, and then use indexOf to find whether the required cache item exists in the keys array.

To sum up, we can use the Storage API provided by uniapp to operate the cache, and determine whether the cache exists through methods such as getStorageSync or getStorageInfoSync. In the process of mobile application development, reasonable use of cache can effectively improve application performance and improve user experience.

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